1. Field of the Invention
The present invention relates to butterfly valves and, more particularly, to butterfly valves having reinforced seat members.
2. Description of the Prior Art
In a conventional butterfly valve, the valve seat against which the disk seals is made of an elastomeric material such as rubber and is disposed in a valve body which generally encircles the valve seat. For example, in U.S. Pat. No. 2,994,342 there is disclosed a butterfly valve in which the valve body has a radially inwardly extending, dovetailed rib, the flexible seat having an annular web with two radially outwardly extending, annular flanges, the web and the flanges defining a radially outwardly opening channel, complementary in shape to that of the rib. Accordingly, when the seat is received in the valve body, there is interlocking between the valve body and the elastomeric seat, the annular web serving also as a reinforcement or backup to the relatively soft resilient seat. Since, in this construction, the valve seat is quite flexible, it can easily be installed in valves which have a one piece body since the seat can be distorted sufficiently to position it in the valve body whereby the rib can be received in the annular channel. Valves constructed in this fashion suffer from the disadvantage that when the disk is in the closed position and the valve is subjected to relatively high differential pressure across the disk, there is a tendency for the resilient rubber seat to be forced into the flow path. In other words, the line pressure can get between the annular rib in the valve body and the relatively soft, pliable seat forcing the seat into the flow path and, in extreme circumstances, perhaps dislodgig the seat from the valve body.
In U.S. Pat. No. 3,233,861, there is shown another butterfly valve construction in which the valve body, rather than having any inwardly extending annular rib, forms a generally smooth cylindrical surface. The annular valve seat is composite in nature being comprised of a rigid, annular ring of a material such as metal, hard plastic or the like, and a resilient, e.g. rubber, annular member which is generally bonded to the inner and end surfaces of the rigid ring. In this construction, the composite seat is slid in and out of the valve body endwise. Moreover, the rigid ring prevents the resilient portion of the seat from being affected by differential line pressure as described above. The disadvantage of this type of valve construction is that when the valve is used in dead-end service, i.e. retaining pressure within a line when the valve is in the closed position and is located at the end of a conduit or the like, it is necessary to secure a flange over the exposed end of the valve in order to retain the composite seat in the valve body because there is no interlocking fit between the valve body and the seat.
It is known to form butterfly valves which have a composite seat structure similar to that discussed above but which also have an interlocking fit between the valve body and the seat such as shown in U.S. Pat. No. 2,994,342. Valves of this type can be used in dead-end service without the necessity for an end flange or the like to retain the seat in the valve body. Such a valve construction is shown, for example, in U.S. Pat. No. 4,225,113. In this type of construction, since the composite seat has a rigid portion which interlocks with the valve body, the seat cannot be distorted to be positioned in the valve body. Accordingly, the valve body is constructed of two sections such that the valve seat can first be positioned in a first section and then the other section of the valve body secured to the first section thereby trapping the composite seat in the valve body.
It would be desirable to have a butterfly valve in which the body was of one piece construction, in which the valve seat was interlocked to the body so the valve could be used in dead-end service, and in which the seat is composite in nature having a rigid reinforcement or backing which prevents the elastomeric portion of the seat from being forced or extended into the flow path under high pressures, by drag of the disk, etc.